Touch it with your fingertips.
Fine cashmere feels soft, smooth, and substantial, even if it’s lightweight.
Pull the sides of the sweater.
They should spring back to the original shape and should not be limp.
Look at the luster.
The sweater should be neither shiny nor dull.
Check for dark fibers in a light-colored sweater (they cannot be seen in a dark one).
These are the coarsest hairs of the cashmere goat and are a sign of inferior quality.